Reports: AC6
44262-AC6 Theoretical Investigations of the Nature of Pi-Pi Interactions
State-of-the-art theoretical methods have been used to probe the fundamental nature of noncovalent interactions involving aromatic groups. Such interactions are central to protein folding, drug docking, crystal packing of organics, self-assembly, etc. We aim to determine the fundamental rules which govern these interactions and, ultimately, to learn how they can be precisely controlled.
1. What is the fundamental nature of pi-pi interactions? In the current grant year, we published the first systematic exploration of how heteroatoms can tune pi-pi interactions (J. Phys. Chem. A). We also published striking evidence (J. Am. Chem. Soc.) that substituent effects in pi-pi interactions cannot be explained based only on electrostatic arguments, as many prior investigators have tried to do. A feature article on pi-pi interactions is in press (J. Phys. Chem. A).
2. Crystalline benzene and the possible importance of three-body interactions. Recent work by Podeszwa has argued that three-body effects contribute up to 10% of the lattice energy of crystalline benzene, far more than our previous estimates indicated. We performed very large CCSD(T) computations to answer this question, and we find that, in basic agreement with our previous (2008) results, three-body effects are worth less than 3.5% of the lattice energy. This article has been submitted.
3. Testing approximate models for pi-pi and other noncovalent interactions. As we have learned much about pi-pi interactions from high-quality studies of model systems, we are now ready to move on to larger and more complex model systems. However, the choice of appropriate theoretical methods is very difficult. We have begun testing a wide variety of approaches for their ability to faithfully reproduce our benchmark-quality CCSD(T) results for a variety of small model systems. One paper (J. Phys. Chem. A, in press) examines a wide variety of methods. Another (J. Comput. Chem.) examines force-field models specifically. Another introduces a spin-component-scaled CCSD method, which performs very well indeed (J. Chem. Phys.)
